Directed by Richard Donner. Starring Bruce Willis and Mos Def. Rated PG.

Although Bruce Willis has long been associated with the Schwarzenegger end of the male-bravado spectrum, his Alan Ladd-like screen persona is usually that of a long-suffering schmo who reluctantly gets drawn into situations where he might be forced to hurt someone and not feel good about it.

In fact, Willis's latest vehicle, the sturdily entertaining 16 Blocks, is directed by Richard Donner-of the Superman and Lethal Weapon movies-to resemble whistle-blower flicks of the 1970s such as Serpico and All the President's Men, even if the script, from Richard Wenk, doesn't have such lofty ambitions. Here, as paunchy, perpetually limping Jack Mosley, the aging action star plays an even more downbeat variation of his Sin City character-?that is, a formerly tough New York detective running out the clock to start his miserable, alcoholic retirement.

On this particular morning, Jack is asked to interrupt his latest hangover to drive small-time thief Eddie Bunker (Mos Def) from jailhouse to courthouse, a distance of 16 blocks. Eddie is due to testify against crooked cops, led by none other than Jack's former partner (St. Elsewhere's David Morse, in quiet-psychopath guise), who is soon gunning for both of them.

This plot is absurd on the face of it. A New York DA running a major case involving half the NYPD wouldn't be taking too many chances with a key witness, and neither would the rotten apples. Still, there's much pleasure in watching Willis as his character gradually grasps the full nastiness of his situation. Even more fun is costar Def, a long-time rapper and already veteran actor. Here, he makes like Jerry Lewis; his Eddie is a squeaky-voiced motormouth with an anecdote or seven for every occasion.

It turns out that Eddie really wants to move to Seattle and open a bakery, and there's more sugary icing near the end, which feels dragged-out after all the gritty, hand-held-camera movement. There's an implication that Eddie is worth saving only because he's so darn nice; it would be more impressive if Jack stuck out his neck for a miserable SOB.